grade-school: Change a UUID to be version 4 (#904)

Upstream: exercism/problem-specifications#1760

Author: ee7

exercises/grade-school/.meta/tests.toml

@@ -4,7 +4,7 @@
 "6d0a30e4-1b4e-472e-8e20-c41702125667" = true
 
 # A student can't be in two different grades
-"dece43c8-3ba5-11eb-8fdf-7f8daeaeb5f2" = true
+"c125dab7-2a53-492f-a99a-56ad511940d8" = true
 
 # Adding more students adds them to the sorted roster
 "233be705-dd58-4968-889d-fb3c7954c9cc" = true